Insights into the effect of complex phosphates on acid-induced milk fan gel properties: Texture, rheological, microstructure, and molecular forces

Milk fan cheese, a type of stretched cheese, presents challenges in its stretch forming. This study investigated the effects of complex phosphates (sodium tripolyphosphate and sodium dihydrogen phosphate, STPP-DSP) on the gelling properties of acid-induced milk fan gel and the mechanisms contributing to its stretch forming. The treatment of milk fan gel with STPP-DSP resulted in improved functional and textural properties compared with the control group. In particular, drawing length increased significantly from 69.67 nm to 80.33 nm, and adhesiveness increased from 1,737.89 g/mm to 1,969.79 g/mm. The addition of STPP-DSP also led to increased viscosity, elastic modulus (G′), and viscous modulus (G″). Microstructural analysis revealed the formation of a fibrous structure within the gel after STPP-DSP treatment, facilitating uniform embedding of fat globules and emulsification. Structural analysis showed that the addition of STPP-DSP increased β-fold and decreased random coiling of the gel, facilitating the unfolding of protein structures. Additionally, UV absorption spectroscopy and excitation emission matrix spectroscopy results indicated the formation of a chelate between STPP-DSP and milk fan gel, increasing protein-protein molecular interactions. Evidence from differential scanning calorimetry and X-ray diffraction demonstrated the formation of sodium caseinate chelate. Fourier transform infrared spectroscopy and zeta potential analysis revealed that the sodium caseinate chelate formed through hydrophobicity, hydrogen bonding, and electrostatic forces. These findings provided theoretical insights into how phosphates can improve the stretch forming of milk fan gel, facilitating the application of phosphate additives in stretched-cheese processing.